Chapter 13. The construction of a sound card

As I have mentioned earlier, sound cards
are extremely complicated to understand and the best of them have an
unbelievable number of functions.

Many of the functions are especially
suitable for solving particular sorts of tasks, and it is very rarely that the
same user needs to use all of them. Let me here name a handful of the very
varied areas:

Recording and mixing of sounds from
instruments/microphones (hard disk recording)

Editing sound files.

Composing with MIDI and special synthesizer
software.

Programming of sound, for example, for games.

Play back of music in stereo or in a surround
format.

Calibration of sound images

Sound for games (stereo or surround).

Sound for active loudspeakers, surround
amplifiers or hi-fi systems.

Conversion of analog recordings (on, for
example, LP records or cassette tape recordings) to mp3, including, if
necessary, the removal of noise.

MiniDisc connection.

All these things
can actually be done with a good sound card and appropriate software, loudspeaker
system, etc. But, as you can probably guess, there are not very many, who need
to use all of them. In the following section, I will try to describe the sound
card’s different components, and what they are used for.

Several components

Fundamentally, a sound card consists of
components like:

A synthesizer.

Conversion devices (Analog/Digital
and Digital/Analog).

A DSP chip.

The first two
devices have, in their own way, something to do with making sound. The third
device (the DSP) is a little computer in itself. It manages coding and decoding
in relation to 3d sounds, surround sound, etc., just like in DVD players, etc.

The sounds

One the sound card’s most basic functions
are to supply ”ready-made” sounds for, for example, games or MIDI melodies. This
also means that the sound card ”contains” sounds, which a computer can make use
of. Sounds like piano, bass, drums, guitar, organ, etc.

It is the sound card’s synthesizer,
which supplies the sounds, and there are several systems. Sounds are created
completely artificially with FM synthesis in the cheapest sound cards (Frequence
Modulation). It is really the right synthesizer principle. The sounds are
synthetic – it sounds a little like a piano, but it isn’t. FM synthesis is
artificial sound and the result sounds like that. Wavetables and Soundfonts
give the best sounds, but they are also a more expensive quality of sound.

The sounds are recordings from real
instruments that are stored either on a sound card or on a hard disk.
Recordings are made with a proper piano and a little sample is made in the
light of the recording. ROM circuits (chips) are found in older sound cards,
which have a permanent content of these samples (wave tables). The
sounds are, so to speak, ”burnt” into the cards.

Figure 65.There are always ”ready-made sounds”
(samples) that the sound card can play back. They are either on the sound card
itself or as a file on the hard disk.

Today the better
sound cards use SoundFont technology. The computer’s hard disk and RAM is made
use of here for the sampled sounds. When the sound card’s software is
installed, a collection of Soundfont files is copied onto the hard disk. From
here they are read into the RAM and “linked” to the sound card.

Figure 66. SoundFonts is an advanced system for the
programming of sound cards with high quality sampled sound. The sounds can be
manipulated with programs like Vienna, which is shown here.

When you play
back, for example, a MIDI melody, then it is the samples, that you listen to.
This can give an extremely fine sound, where a piano really sounds like a
genuine piano. All the better sound cards use both synthetic and sampled
sounds, just like the electric pianos you can buy in music shops also do.

Playing a MIDI file on a computer can
easily test a sound card’s fundamental quality. We shall be looking more
closely at the concept MIDI, which works with music files without sound.
When a MIDI file is played back, then it is the sound card’s own sound, which
is played and it is, therefore, very easy to hear the difference between the
various sound cards.

D/A conversion for playing back

The sound card is a link – a bridge, one
could say – between the purely digital computer and the analog sound. This
means, that you can direct analog, electrical sound signals into a computer and
get them digitised. And the other way around the digital sounds can also be converted
to analog sound signals in the sound card. Both conversions are made in the
sound card in small DAC- and ADC chips (see earlier in the booklet, e.g. page 3).

Figure 67. The
converter (DAC), which converts digital sound data to analog signals on Sound
Blaster Audigy sound cards. The opposite conversion
takes place on a corresponding ADC chip in the card.

D/A conversion is
used when a sound card is used as a player. If it, for instance, is
connected to a CD drive, then you can play a normal music CD. The digital
soundtrack is directed from the CD drive via the motherboard to the sound card,
where it is converted to analog signals.

The analog signals correspond to the ports
from a headset port on a television or a radio. The signal can be sent directly
to a set of headphones, which is very practical, in the case of sound from a
computer. The signal can also be connected to a stereo amplifier or to a set of
active loudspeakers.

A/D conversion for recording

A/D conversion is used correspondingly when
you record sound on a computer. The sound signal is fetched from the
sound card’s analog port. The signals are sampled and converted into data.

Every analog source of sound can be
digitised with a sound card. That is to say, you can fetch sounds from a radio,
a record player, a tape recorder, a video, a television, a microphone, electric
instruments, etc. Anything, that has a headphone or a line port, can, in
reality, be connected to the sound card’s analog port.

You have to be aware, however, of the fact
that a record player’s signal is very weak. Which is why an additional amplifier
has to be added (an RIAA amplifier, a little black box), which amplifies the
signal up to the level expected by the sound card’s port. Read more about this
in the IDG booklet ”Computer Audio”. The signal from TAPE OUT on a stereo
loudspeaker or receiver can be directly connected to the sound card’s port LINE
IN.

The result of the digitizing can be sound
data, which is either ”raw” or uncompressed or sound files, which are packed
into, for instance, the mp3 format. This is dependent on which program you use
to make the recording.

Analog and digital plugs

So we have seen that the sound card’s A/D
and D/A converters are used every time you either record or play back a sound
with the help of analog devices. Of course, there has to be plugs on the sound
card to enable the connection of these devices.

There ought to be two or three minijack
plugs, functioning as analog ports (LINE IN and MIC) or (LINE OUT or SPEA­KERS).
Or else there will be digital plugs like the earlier mentioned optic port
(TOSLink).

Figure 68. On the left you can see the optical,
digital plug. The three other plugs are used for the analog devices. See also Figure 60 on page 3.

A sound card has
a lot of other plugs than those mentioned here. In the next chapter, we will
look at an example of a sound card and its options for connection.

Quality

The quality of a sound card’s D/A and A/D
converters can vary a lot. With the cheapest sound cards, you can only convert
PCM sounds, that are sampled with 44,1 kHz and a 16 bit resolution, while the
better sound cards can manage much more powerful samples. All things
considered, there really is a lot of difference in sound quality with regard to
different D/A converters.

If musicians use a sound card for hard disk
recordings, then it is important that the sound card has a powerful A/D
converter, so that the sound can be recorded with the best possible quality.
This is also necessary if the sound card is to be used for playing high quality
Surround sound (e.g. DVD-Audio) via an active loudspeaker set.

Luckily, sound cards of good quality are
not terribly expensive. Creative’s Sound Blaster Audigy cards are found in many
designs with a starting price less than 1000 kr. The models differ in how many
plugs and connections they have, and how much software they are accompanied
with.

You can find extensive sound guides on the
Internet (see the addresses on page 3), where the different cards are tested and compared. There, you can
see that a card like Sound Blaster’s top model Audigy2 Platinum eX is
close to being able to be compared with top professional cards like, for
example, LynxTWO (Figure 70).

Figure 70. High end sound card used in music
studios. Price: about $1000.